1. Field of the Invention
The present invention relates to a charging apparatus. More specifically, the present invention relates to a charging apparatus for charging a rechargeable battery adapted for charging in succession and individually a plurality of rechargeable batteries.
2. Description of the Prior Art
Conventionally a series charging system has been proposed as a system for charging a plurality of rechargeable batteries. According to a series charging system, a charging current of the same magnitude is applied to a plurality of series connected batteries. Accordingly, a problem is involved in the series charging system that if and when the remaining quantity of electricity is different from battery to battery one is overcharged while the other is undercharged, with the result that all the batteries cannot be equally charged. In order to eliminate such problem encountered in the series charging system, a parallel charging system may be considered. According to such parallel charging system, a charging current is individually applied to each of a plurality of batteries connected in parallel. Therefore, such parallel charging system requires that a charging completion detecting means necessary in rapid charging, in particular, is provided for each of the batteries, which entails another problem that a charging apparatus itself becomes expensive and large sized.
On the other hand, it has been well-known that a gas tight sealed battery such as a nickel-cadmium battery exhibits a charging characteristic as shown in FIG. 1. The charging quantity characteristic of such gas tight sealed battery exhibits a change as shown by the curve B in FIG. 1, in which the saturated state is a fully charged state of the battery. The charging voltage characteristic of such gas tight sealed battery is shown by the curve A in FIG. 1, which exhibits an increase until a peak (as denoted as a) shortly before a fully charged state is reached and thereafter exhibits a gradual decrease until a fully charged state is reached. Therefore, if and when a simple approach is employed to interrupt a charging current by detecting a charged state of a battery in rapid charging as described previously, an overcharged state or an undercharged state results. Therefore, a specific charging state detecting means is required for detecting a charging completion in accordance with the above described charging characteristic by detecting a battery voltage, a temperature and/or an internal gas pressure, for example. In the case of the above described parallel charging system, such charging state detecting means is required for each of the batteries and again the apparatus becomes expensive and large sized.